Trigonometric wave generation circuit using series expansion

Abstract

A DTMF signal generating circuit is provided with a frequency designating unit which designates frequencies to form a DTMF signal, a sinusoidal wave computing unit which computes sinusoidal waves by referring to frequencies designated by the frequency designating unit, and a sinusoidal wave synthesizing unit which synthesizes two sinusoidal waves computed by the sinusoidal wave computing unit. The sinusoidal wave computing unit is provided with operators such as an adder-subtracter and a multiplier and generates a sinusoidal wave by determining terms of a Taylor expansion of a sinusoidal function by arithmetic operation.

1 . A trigonometric wave generating circuit comprising an operator which determines terms of a series expansion of a trigonometric function by direct arithmetic operation, so as to generate a trigonometric wave.  
   
   
       2 . The trigonometric wave generating circuit according to  claim 1 , further comprising a memory which holds coefficients of the terms of the series expansion of the trigonometric function.  
   
   
       3 . The trigonometric wave generating circuit according to  claim 1 , wherein the operator performs the operation after bounding the phase of the trigonometric function to fall within a range from −½π to ½π by a shift operation.  
   
   
       4 . The trigonometric wave generating circuit according to  claim 2 , wherein the operator performs the operation after bounding the phase of the trigonometric function to fall within a range from −½π to ½π by a shift operation.  
   
   
       5 . A dual tone multi-frequency signal generating circuit comprising: 
 a first frequency sinusoidal wave generating unit which computes a sinusoidal wave of a first frequency using a series expansion;    a second frequency sinusoidal wave generating unit which computes a sinusoidal wave of a second frequency using a series expansion; and    a sinusoidal wave synthesizing unit which synthesizes the sinusoidal wave computed by the first frequency sinusoidal wave generating unit and the sinusoidal wave computed by the second frequency sinusoidal wave generating unit.    
   
   
       6 . The dual tone multi-frequency signal generating circuit according to  claim 5 , wherein the first frequency sinusoidal wave generating unit and the second frequency sinusoidal wave generating unit are formed to share a single trigonometric wave generating circuit according to  claim 1 .  
   
   
       7 . The dual tone multi-frequency signal generating circuit according to  claim 6 , further comprising a frequency designating unit which designates the first frequency and the second frequency to the single trigonometric wave generating circuit.  
   
   
       8 . A sound signal generating circuit comprising: 
 the dual tone multi-frequency signal generating circuit according to  claim 5;     an acoustic signal generating unit which generates a digital acoustic signal; and    a mixing unit which mixes the digital dual tone multi-frequency signal generated by the dual tone multi-frequency signal generating unit with the digital acoustic signal generated by the acoustic signal generating unit.    
   
   
       9 . A sound signal generating circuit comprising: 
 the dual tone multi-frequency signal generating circuit according to  claim 6;     an acoustic signal generating unit which generates a digital acoustic signal; and    a mixing unit which mixes the digital dual tone multi-frequency signal generated by the dual tone multi-frequency signal generating unit with the digital acoustic signal generated by the acoustic signal generating unit.    
   
   
       10 . A sound signal generating circuit comprising: 
 the dual tone multi-frequency signal generating circuit according to  claim 7;     an acoustic signal generating unit which generates a digital acoustic signal; and    a mixing unit which mixes the digital dual tone multi-frequency signal generated by the dual tone multi-frequency signal generating unit with the digital acoustic signal generated by the acoustic signal generating unit.    
   
   
       11 . The sound signal generating circuit according to  claim 8 , further comprising: 
 an interpolator which interpolates between values of the sound signal mixed by the mixing unit;    a ΔΣ D/A converter which subjects an output signal from the interpolator to digital-to-analog conversion; and    a filter provided in a stage subsequent to the ΔΣ D/A converter.    
   
   
       12 . The sound signal generating circuit according to  claim 9 , further comprising: 
 an interpolator which interpolates between values of the sound signal mixed by the mixing unit;    a ΔΣ D/A converter which subjects an output signal from the interpolator to digital-to-analog conversion; and    a filter provided in a stage subsequent to the ΔΣ D/A converter.    
   
   
       13 . The sound signal generating circuit according to  claim 10 , further comprising: 
 an interpolator which interpolates between values of the sound signal mixed by the mixing unit;    a ΔΣ D/A converter which subjects an output signal from the interpolator to digital-to-analog conversion; and    a filter provided in a stage subsequent to the ΔΣ D/A converter.    
   
   
       14 . A communication apparatus comprising the audio signal generating circuit according to  claim 8 .  
   
   
       15 . A communication apparatus comprising the audio signal generating circuit according to  claim 11.